A secondary battery (e.g., a nonaqueous electrolyte lithium secondary battery) or a capacitor is provided with a tab lead for taking out electricity. Conventionally, an aluminum plate was used as a positive tab lead, and a copper plate was used as a negative tab lead (see Patent Document 1).
In the case of using such a battery as a power source for, e.g., an automobile, it is required to take out a large current, and therefore a plurality of unit cells are electrically connected to constitute an assembled battery. In other words, the electrode terminals (tab leads) of a plurality of unit cells are connected to constitute an assembled battery. In many cases, conventionally, such a tab lead connection was performed by welding.